Dissection of the Phoca cristata. 101 



vided at its middle entirely around, its two edges connected 

 by an elastic membrane thickly covered by muscles. The 

 posterior half is subdivided into four longitudinal segments, 

 extending from its edge to within a quarter of an inch of the 

 entrance of the optic nerve. 



This structure, by elongating the axis of vision, may enable 

 the animal more clearly to discern distant objects, and also 

 by the reverse to draw the eye deep within the socket during 

 repose, especially as there are no moveable lids, but only 

 the membrana nictitans. 



The lens is spherical, the iris broad and evidently muscular. 



The penis strongly resembling that of the dolphin and 

 porpoise, but containing a cylindrical bone seven inches long, 

 with a small groove on its under side* 



Testicles very large, and strongly exhibiting the corpus 

 pampiniforme. They were without the pelvis, and the size 

 of the abdominal ring compared with that of the testis, forbade, 

 all belief that they could ever repass into the abdomen, unless 

 very much lessened in size. 



The os hyoides has a delicate body, slightly semilunate, with- 

 out tuberosity or apophysis. The posterior cornua complete 

 the arch, these are flattened, and gradually increasing in 

 width, as they approach the thyroid cartilage, they terminate 

 in a rounded obtuse extremity. 



The anterior cornu is composed of three bones, the first of 

 which is short and thick, the middle one has a large base, 

 gradually tapering towards its junction with the third, which 

 in length and delicacy exceeds the others, being cylindrical 

 in its body, and condyloid in its termination. 



The aretenoid cartilages were unusually large and long, 

 and from the nature of their joint, admit of motion in all 

 directions ; and it will be well here to remark, that the closing 

 of the rirna glottidis is effected by a peculiar cartilaginous 

 structure. There was also a peculiarity in the muscular 

 structure of this part worthy of note, for the aretenoidcei 



