14 PROF. T. JEFFEEY PARKER ON THE 



antorbital process of the cranium. The first has an irregular outline, and is continued 

 forwards by a process which forms the lower boundary of the nostril ; the second is 

 nearly oblong in outline. These are the only representatives of the suborbital chain 

 of bones so c°ommon in Teleosts. They are both subcutaneous {cf. fig. 1). 



2. The Suspensorium and the Upper and Lower Jaws. 

 (Plate IV. fig. 6, & V. figs. 14-16.) 

 These bones, although many of them are of peculiar form, do not differ from the 

 ordinary teleostean type to anything like the same extent as those of the cranium. 



The Injomandilular (h.m) is an irregular bone articulating by a dilated proximal 

 extremity or head with a sigmoid groove on the outer surface of the auditory capsule 

 (cf. figs. 6, 7, and 15), and ending distally in a sharply truncated extremity. Imme- 

 diately below the head, near the posterior border of the bone, is an oval facet (fig 15, 

 opi) covered with cartilage, for articulation with the opercular (cf. figs. 6 and 14). 



The sympJedic [sy) is a small rod-like bone, truncated at its proximal, pointed at its 

 distal end, separated by a cartilaginous interval from the hyomandibular, and fitting 

 into a groove on the inner face of the quadrate (fig. 15, ^u). 



The quadrate (qu) is a triangular bone, with its lower or distal angle produced into a 

 process which bears the glenoid cavity for the articulation of the mandible. It 

 articulates by its anterior edge with the pterygoid {]3t), while its slightly curved dorsal 

 border passes into a thin plate of cartilage with a sinuous dorsal edge, evidently the 

 remains of the embryonic palato-pterygoid process of the mandibular arch (fig. 15). 



The pterygoid (pt) is a narrow bone placed nearly vertically; its posterior border 

 articulates with the quadrate and mesopterygoid {mspt}, its upper border with the 

 palatine (pi). 



The mempteryyoid [ms.pt) is a very thin and irregular bony plate, closely connected 

 with the inner surface of the plate of cartilage mentioned above, but extending con- 

 siderably beyond its dorsal edge. The mesopterygoid is marked by radiating lines 

 which start from a point altogether above the cartilage (fig. 15) ; the latter is, in its 

 dorsal portion, easily separable from the contiguous bone, but lower down the two 

 become inseparably united (fig. 14). I should judge from these facts that the meso- 

 pterygoid, unlike its homologue iu the Salmon, commences as a parostosis, the 

 ossification afterwards extending into the cartilage and becoming ectosteal. This, if 

 true, is decidedly interesting, since the pterygoid of many of the higher Vertebrata, 

 from Amphibia to Mammals, is parosteal. 



The metapterygoid [mpt) is a triangular bone, articulating by its base with the 

 mesopterygoid and pterygoid cartilage, and passing upwards and backwards along the 

 anterior edge of the hyomandibular. 



The palatine (pi) is a short irregular bone, rather broader than long, uniting by 

 suture with the pterygoid and mesopterygoid, and articulating by a large facet with 

 the antorbital process of the cranium. 



