TYLOTOTRITON. 851 



Srd caudal, tlie transverse process becomes flattened from before backwards, and 

 tbe bypapopbyses spring from it and from tbe centrum as a common base in a mucb 

 more perfect manner tban occurs in tbe 1st caudal ver^bra of Siren, as described 

 by Miyart. 



Tbe bypaxial arcb, figs. 15 to 18 m and n, consists of a broad flat plate, witb two 

 diverging processes posteriorly. In tbe 4tb caudal vertebra, a prominent ridge is 

 developed on tbe anterior face of tbe plate, wbicb is curved witb its convexity 

 forwards ; and tbis modification becomes more and more intensified, until at last, 

 in tbe middle of tbe tail, fig. 16 m, the ridge is converted into a broad tbin lamina, 

 witb two divergent plates, wbicb serve to embrace tbe ridges of tbe arcb bebind. 



The ribs. — Tbere are sixteen ribs, tbirteen in tbe dorsal, one in tbe sacral, and 

 two in tbe caudal region. Eacb rib is supported on a double-beaded transverse 

 process, and is capable of a certain amount of mobility. As tbe ribs are traced back- 

 wards, tbe tubercular and capitular portions are less distinctly marked, as is also tbe 

 division of tbe transverse processes into dorsal and ventral sections. Tbe ribs are 

 well developed in tbe five anterior vertebrae, and are moderately curved, but tbe suc- 

 ceeding ribs are nearly straight. Tbe proximal ends of tbe ribs, figs. 19, 20, are 

 flattened from before backwards, and each consists of a capitular and tubercular 

 process, separated from eacb other by a narrow interval, except in those in which 

 these parts tend to become confluent. A considerable process (figs. 19, 20, &c., p) 

 is developed on the posterior margin of eacb of the first five ribs. All of these rib 

 processes, with the exception of the first, terminate in the knob-like glands of the 

 side, and the free extremities of the remaining ribs end in the same structures. The 

 first rib Hes under the scapula, and has no gland opposite to it. The sacral rib, 

 figs. 11 and 12 m, has such a strong resemblance to its transverse process that it 

 might be mistaken for such, and from its nature has of course no relations witb the 

 lateral glands. 



Scapular arch. — The scapular arch lies over tbe 1st rib and on the anterior fourth 

 of the 2nd between the 2nd and 3rd vertebrae. All the constituent bones are com- 

 pletely united with one another. The coracoid element is a semicu'cular flattened 

 rather thick plate (fig. 41), separated from its fellow by the semi-osseous epicoracoid 

 flaps which overlap each other. The glenoid cavity is behind the line of the 

 scapula on the posterior and superior margin of tbe coracoid, and looks upwards, 

 backwards and outwards, and is triangular with its base upwards. It has two 

 protuberant walls ; but the upper and posterior margins are continuous with the 

 posterior margin of the coracoid, and scooped out into a deep wide notch, closed in 

 tbe recent state by a strong membrane. The lateral margins are separated from 

 each other anteriorly by a narrow notch for the reception of the articulating ridge 

 of the humerus. There is a nerve foramen in the usual position in front of the 

 glenoid cavity and a deep notch at the base of the anterior angle of the scapula 

 and coracoid. The scapular element is slightly concave externally, and expanded 

 from below upwards terminates in a broad semi-osseous or cartilaginous supra- 

 scapula without any notch on its anterior angle. 



