Some descriptive excerpts from
Harry Potter and the Prisoner of Azkaban:
 (All references are to the American trade paperback edition)

Chapter 2, page 16-7:
     "...The public is warned that Black is armed and extremely dangerous.  A special hot line has been set up, and any sighting of Black should be reported immediately."
     "No need to tell us he's no good," snorted Uncle Vernon, staring over the top of his newspaper at the prisoner.  "Look at the state of him, the filthy layabout!  Look at his hair!"
     He shot a nasty look sideways at Harry, whose untidy hair had always been a source of great annoyance to Uncle Vernon.  Compared to the man on the television, however, whose gaunt face was surrounded by a matted, elbow-length tangle, Harry felt very well groomed indeed.

Chapter 2, page 38:
     Harry looked into the shadowed eyes of Sirius Black, the only part of the sunken face that seemed alive. Harry had never met a vampire, but he had seen pictures of them in his Defense Against the Dark Arts classes, and Black, with his waxy white skin, looked just like one.

Chapter 10, page 204:
     [professors reminiscing about Harry's father] "Precisely," said Professor McGonagall.  "Black and Potter.  Ringleaders of their little gang.  Both very bright, of course -- exceptionally bright, in fact -- but I don't think we've ever had such a pair of trouble-makers --"

***
     "You'd have thought Black and Potter were brothers!" chimed in Professor Flitwick.  "Inseparable!"
     "Of course they were," said Fudge.  "Potter trusted Black beyond all his other friends. Nothing changed when they left school.  Black was best man when James married Lily.  Then they named him godfather to Harry.  Harry has no idea, of course.  You can imagine how the idea would torment him."
     "Because Black turned out to be in league with You-Know-Who?" whispered Madam Rosmerta.

Chapter 11, page 212:
     [Harry] stopped on a picture of his parents' wedding day.   There was his father waving up at him, beaming, the untidy black hair Harry had inherited standing up in all directions.  There was his mother, alight with happiness, arm in arm with his dad.  And there ... that must be him.  Their best man ... Harry had never given him a thought before.
     If he hadn't known it was the same person, he would never have guessed it was Black in this old photograph.  His face wasn't sunken and waxy, but handsome, full of laughter....  Did he realize he was facing twelve years in Azkaban, twelve years that would make him unrecognizable?

Chapter 14, page 270:
[Sirius has attacked Ron Weasley] "...I was asleep, and I heard this ripping noise, and I thought it was in my dream, you know?  But then there was this draft ... I woke up and one side of the hangings on my bed had been pulled down ... I rolled over ... and I saw him standing over me ... like a skeleton, with loads of filthy hair ... holding this great long knife, must've been twelve inches ...."

Chapter 17, page 338-9:
     Ron was staring over Harry's shoulder.  Harry wheeled around. With a snap, the man in the shadows closed the door behind them.
     A mass of filthy, matted hair hung to his elbows.   If eyes hadn't been shining out of the deep, dark, sockets, he might have been a corpse. The waxy skin was stretched so tightly over the bones of his face, it looked like a skull. His yellow teeth were bared in a grin.   It was Sirius Black.

***
     "I thought you'd come and help your friend," he said hoarsely.  His voice sounded as though he had long since lost the habit of using it.  "Your father would have done the same for me.  Brave of you, not to run for a teacher.  I'm grateful ... it will make everything much easier...."

Chapter 17, page 341:
     Black was sprawled at the bottom of the wall.   His thin chest rose and fell rapidly as he watched Harry walking slowly nearer, his wand pointing straight at Black's heart.
     "Going to kill me, Harry?" he whispered.
     Harry stopped right above him, his wand still pointing at Black's chest, looking down at him.  A livid bruise was rising around Black's left eye and his nose was bleeding.
     "You killed my parents," said Harry, his voice shaking slightly, but his wand hand quite steady.
     Black stared up at him out of those sunken eyes.
     "I don't deny it," he said very quietly.  "But if you knew the whole story."
     "The whole story?" Harry repeated, a furious pounding in his ears.  "You sold them to Voldemort.  That's all I need to know."
     "You've got to listen to me," Black said, and there was a note of urgency in his voice now.  "You'll regret it if you don't ... You don't understand...."

Chapter 17, page 343-5:
     Then Lupin spoke, in a very tense voice.
     "Where is he, Sirius?"
     Harry looked quickly at Lupin.  He didn't understand what Lupin meant.  Who was Lupin talking about?  He turned to look at Black again.
     Black's face was quite expressionless.  For a few seconds, he didn't move at all.  Then, very slowly, he raised his empty hand and pointed straight at Ron.  Mystified, Harry glanced around at Ron, who looked bewildered.

***
...Lupin's eyes suddenly widened, as thought he was seeing something beyond Black, something none of the rest could see, "--unless he was the one ... unless you switched ... without telling me?"
     Very slowly, his sunken gaze never leaving Lupin's face, Black nodded.

***
Lupin was lowering his wand, staring fixedly at Black.  The Professor walked to Black's side, seized his hand, pulled him to his feet... and embraced Black like a brother.

Chapter 18, page 350:
     "All right, then," Black said, without taking his eyes off the rat.  "Tell them whatever you like.   But make it quick, Remus.  I want to commit the murder I was imprisoned for...."

Chapter 19, page 370-2:
     [Hermione:] "If you don't mind me asking, how -- how did you get out of Azkaban, if you didn't use Dark Magic?"

***
     ...Black was frowning slightly at Hermione, but not as though he were annoyed with her.  He seemed to be pondering his answer.
     "I don't know how I did it," he said slowly.  "I think the only reason I never lost my mind is that I knew I was innocent.   That wasn't a happy thought, so the dementors couldn't suck it out of me... but it kept me sane and knowing who I am ... helped me keep my powers ... so when it all became ... too much ... I could transform in my cell ... become a dog.  Dementors can't see, you know...."  He swallowed.   "They feel their way toward people by feeding off their emotions....   They could tell that my feelings were less -- less human, less complex when I was a dog ... but they thought, of course, that I was losing my mind like everyone else in there, so it didn't trouble them...."

[on realising the traitor was still alive]

     "It was as if someone had lit a fire in my head, and the dementors couldn't destroy it ... It wasn't a happy feeling ... it was an obsession ... but it gave me strength, it cleared my mind."

Chapter 19, page 372:
     "Believe me," croaked Black.  "Believe me, Harry.   I never betrayed James and Lily.  I would have died before I betrayed them."

Chapter 19, page 373:
     "Not if he thought I was the spy, Peter," said Lupin.   "I assume that's why you didn't tell me, Sirius?" he said casually over Pettigrew's head.
     "Forgive me, Remus," said Black.
     "Not at all, Padfoot, old friend," said Lupin, who was now rolling up his sleeves.  "And will you, in turn, forgive me for believing you were the spy?"
     "Of course," said Black, and the ghost of a grin flitted across his gaunt face.  He, too, began rolling up his sleeves.   "Shall we kill him together?"
     "Yes, I think so," said Lupin grimly.

Chapter 19, page 375:
     "What was there to be gained by fighting the most evil wizard who has ever existed?" said Black, with a terrible fury in his face.   "Only innocent lives, Peter!"
     "You don't understand!" whined Pettigrew.  "He would have killed me, Sirius!"
     "THEN YOU SHOULD HAVE DIED!" roared Black.   "DIED RATHER THAN BETRAY YOUR FRIENDS, AS WE WOULD HAVE DONE FOR YOU!"

Chapter 20, page 378-9:
     "You know what this means?" Black said abruptly to Harry as they made their slow progress along the tunnel.  "Turning Pettigrew in?"
     "You're free," said Harry.
     "Yes...," said Black. "But I'm also -- I don't know if anyone ever told you -- I'm your godfather."
     "Yeah, I knew that," said Harry.
     "Well ... your parents appointed me your guardian," said Black stiffly.  "If anything happened to them..."
     Harry waited.  Did Black mean what he thought he meant?
     "I'll understand, of course, if you want to stay with your aunt and uncle," said Black.  "But ... well ... think about it.   Once my name's cleared ... if you wanted a ... a different home..."
     "What -- live with you?" he said, accidentally cracking his head on a bit of rock protruding from the ceiling.  "Leave the Dursleys?"
     "Of course, I thought you wouldn't want to," said Black quickly.  "I understand, I just thought I'd --"
     "Are you insane?" said Harry, his voice easily as croaky as Black's.  "Of course I want to leave the Dursleys!"

***
     "You want to?" [Black] said. "You mean it?"
     "Yeah, I mean it!" said Harry.
     Black's gaunt face broke into the first smile Harry had seen upon it.  The difference it made was startling, as though a person ten years younger were shining through the starved mask; for a moment, he was recognizable as the man who had laughed at Harry's parents' wedding.

From Harry Potter and the Goblet of Fire:

Chapter 19, page 331:
     Sirius looked different from Harry's memory of him.   When they had said good-bye [at the end of Prisoner of Azkaban], Sirius's face had been gaunt and sunken, surrounded by a quantity of long, black, matted hair -- but the hair was short and clean now, Sirius's face was fuller, and he looked younger, much more like the only photograph Harry had of him, which had been taken at the Potters' wedding.

***
     Sirius looked at him, eyes full of concern, eyes that had not yet lost the look that Azkaban had given them - that deadened, haunted look....

Chapter 27, page 521:
...Harry, however, was looking at the black dog, which had just turned into his godfather.
     Sirius was wearing ragged gray robes; the same ones he had been wearing when he had left Azkaban.  His black hair was longer than it had been when he had appeared in the fire, and it was untidy and matted once more.  He looked very thin.
     "Chicken!" he said hoarsely after removing the old Daily Prophets from his mouth and throwing them down onto the cave floor.
     Harry pulled open his bag and handed over the bundle of chicken legs and bread.
     "Thanks," said Sirius, opening it, grabbing a drumstick, sitting down on the cave floor and tearing off a large chunk with his teeth.   "I've been living off rats mostly.  Can't steal too much food from Hogsmeade; I'd draw attention to myself."
     He grinned up at Harry, but Harry returned the grin only reluctantly.
     "What're you doing here, Sirius?" he said.
     "Fulfilling my duty as godfather," said Sirius, gnawing on the chicken bone in a very doglike way.  "Don't worry about it, I'm pretending to be a lovable stray."

Chapter 27, page 528:
     Sirius let out a laugh that was much more like a bark.

Chapter 36, page 693-4:
     Dumbledore... and Harry went up the moving spiral staircase to the oak door.  Dumbledore pushed it open.  Sirius was standing there.  His face was white and gaunt as it had been when he escaped Azkaban.  In one swift movement, he had crossed the room.

Chapter 36, page 698:
     "Your parents?" said Dumbledore quietly.
     "Yes," said Harry.
     Sirius's grip on Harry's shoulder was now so tight it was painful.
     "The last murders the wand performed," said Dumbledore, nodding. "In reverse order...."

***

...how the shadow of Harry's father had told him what to do...
     At this point, Harry found he could not continue.   He looked around at Sirius and saw that he had his face in his hands.

Chapter 36, page 712:
     The great black dog looked up at Dumbledore, then, in an instant, turned back into a man.

***
     "Him!" [Snape] snarled, staring at Sirius, whose face showed equal dislike.  "What is he doing here?"
     "He is here at my invitation," said Dumbledore, looking between them, "as are you, Severus.  I trust you both.  It is time for you to lay aside your old differences and trust each other."
     Harry thought Dumbledore was asking for a near miracle.   Sirius and Snape were eyeing each other with the utmost loathing.

Last revised Sept. 6, 2002