376 STRUCTURE OF VERTEBRATES. 



DIAGRAM XXI. 

 Skeleton. 



Skull I. (after Wiedersheim) shows the endofthenotochord (notoch.), 

 the parachordals {pa.), the trabeculas (tr.). The nasal capsule («fl.), 

 the position of the eye [opt. ). , and the auditory capsule {aud. ), are also 

 shown. 



In Skull II. (after Wiedersheim) the chondrocranium is developed. 

 There is an unclosed region or fontanelle on the roof. 



Below Skull I. is a figure marked Ribs. It represents (after Huxley) 

 the skeleton in the thoracic region of a crocodile, and shows the centrum 

 (c.) of a vertebra, the transverse processes (/./.), the neural spine («. s.), 

 the articular processes (z. z.), the tubercle {(.) and the capitulum (ra/.) 

 of a rib, the upper portion of a rib {v. r.) bearing an uncinate process 

 (p. «.), the cartilaginous (shaded) lower portion of the rib, the ventral 

 sternum (.r^. ), and the so-called sternal ribs (it. r. ) connecting ribs and 

 sternum. 



Below this is a diagrammatic pectoral girdle, showing the relative 

 positions of ventral coracoid {cor.), clavicle {clav.), and dorsal scapula 

 {scap. ). 



To the right is the pelvis of a crocodile with dorsal ilium (//. ), ventral 

 and anterior pubis {pub. ), ventral and posterior ischium {isch. ). 



Ck. I. represents an unconstricted notochord surrounded by its 

 sheath {sh. ). 



Ch. 2. (after Gegenbaur) shows the vertebral constriction of the 

 notochord by its sheath. The dark intervertebral parts {i. v. ) indicate 

 the limits of the resulting vertebras. 



Ch. 3. (after Gegenbaur) shows the intervertebral constriction of the 

 notochord as it occurs in Amphibians. 



Ch. 4. (after Balfour) shows a cross section of the vertebral column in 

 a young Elasmobranch. The notochord {notoch.), its sheath {sh.), the 

 neural arches («. a.), enclosing the spinal cord {s. c), and the hjemal 

 arches {h. a.), are shown. 



