REPTILES. 123 



running forwards on both faces of the cartilaginous plate. The whole of the coracoid mass is 

 thrice the breadth and half the height of the scapula; it is of considerable thickness, and is 

 pierced by the cutaneous nerve as usual (c. fo.), but there is no " fenestra." Thus we see that 

 this Shoulder-girdle is less developed than that of CMrotes 1 , vhich has the supra-scapula endos- 

 teally ossified, and the development of the scapular and coracoid shafts much more perfect. 

 Altogether, this is scarcely in advance of what is seen in the Urodelous Amphibia. 



In my specimen the ossification, as well as the morphological condition of the Sternum, is 

 very much in advance of that (or those) dissected by Rathke ; this may partly be accounted for 

 by supposing a difference of age, but is, I have no doubt, mainly attributable to individual differ- 

 ence : moreover, the two halves of the body may vary very considerably. The Sternum (Plate XI, 

 fig. 5) has quite a Mammalian character, like that of Chirotes (Plate VIII, fig. 8), but more advanced, 

 and having proper costal hoops connected with it. The manubrium (prse-sternum, p. st.) is 

 arrow-shaped ; it becomes suddenly narrow in front of the first pair of thoracic ribs, and behind 

 them is strongly notched on both sides : this constriction answers to the transverse cleft so 

 constant in the Mammalian Sternum. There is behind this semi-cloven part an elegant, narrow 

 continuation (m. st., x. st.), having three equidistant enlargements; with the first and second of 

 these the second and third thoracic ribs articulate by synovial joints : the last enlargement is the 

 bilobate extremity of the xiphisternum (x. st.). Contrary to what Rathke describes, we have 

 here the usual right and left double endosteal plates ; these are deficient along the mid-line and 

 coracoid lips (p. st.) : these plates are very thin, and have cartilage in considerable quantity, both 

 between them as a pith and outside them as a bark. There is a sternal rib attached behind 

 the left coracoid groove (figs. 4, 5) ; this is attached by fibrous tissue to the pointed, soft 

 end of the long rib growing from the fourth cervical vertebra ; the three before it have no free 

 ribs : behind this comes the long rib of the fifth cervical ; this has a rudimentary sternal 

 piece continuous with it, which is free, and is hooked backwards (fig. 4). On the right side 

 (fig. 5) no distal sternal piece occurs. Behind the xiphisternum there are seven pairs tot floating 

 ribs that become fixed by growing towards each other, and have united by suture at the mid-line, 

 all save the first pair (ar. 1), for these coalesce with each other, and grow forwards into a supple- 

 mentary sternal plate ("metasternum"); this part (m. t. s.) is shown twice the natural size, and 

 also magnified eight diameters in fig. 5. The little "metasternal" plate is wedge-like, emarginate 

 in front, and concave behind: it has its own "endosteal" Iamina3, and is therefore considerably 

 differentiated as a separate morphological element. Behind these seven highly elastic costal 

 hoops there are three pairs of ribs that do really float; but they have their "abdominal" counter- 

 parts, although at a considerable distance from the vertebral portion (see fig. 4, r. 13 15): 

 the last of these are very small, but they meet at the mid-line (fig. 5, r. 15). The "costa 

 intermedia" (i. r.) attains its highest development here (see fig. 6, which shows that of the 

 second thoracic arch of the right side magnified eight diameters) ; it is a heart-shaped mass, very 

 nearly severed from the vertebral rib above, and from the sternal rib below. The vertebral 

 shaft-bone (v. r.) nearly reaches to the upper transverse cleft ; the endosteal tube (filled and 

 covered with soft cartilage) of the sternal rib (s. r.) nearly reaches the lower, narrow isthmus : as 

 for the "intermediate rib," it has its own endosteal ring. 



Rathke (p. 125) speaks of the common Chameleon as having two pairs of ribs attached to the 

 larger anterior part of the Sternum, and one pair to the smaller posterior part : in C. pumila 

 he found two to the anterior and none on the posterior part. There must be great variability in 



