THE SKULL OF CHIMJSRA. 



119 



shelf which transmits the arteria carotis externa and the ramus 

 palatums facialis, these two foramina, being persisting remnants 

 of the palatoquadrate fissure of Dean's (1906, p. 108) descriptions 

 of embryos. That fissure of embryos lies, as shown in Dean's 

 figures, between the palatoquadrate, the trabecula, and the 

 anterior edge of a shelf of cartilage that projects laterally from 

 the neurocranium beneath the hind end of the orbit and is 

 fused, in its antero-lateral portion, with the palatoquadrate. 

 The vena jugularis accordingly lies definitely ventral to this 

 laterally projecting shelf-like process of the neurocranium, and 

 hence also morphologically ventral and internal to the dorso- 

 posterior portion of the palatoquadrate. If then this shelf-like 

 process is an outgrowth of the neurocranium, the dorso-posterior 

 end of the palatoquadrate, as shown by Dean, must be the 

 processus oticus of that cartilage, but it seems much more 

 probable that the shelf itself is the processus oticus, or extra- 

 branchial element of the arch. Dean (I. c. p. 129) considers this 

 shelf to be the posterior portion of the pharyngeal element of 

 the mandibular arch, but in that case this element of the arch 

 has fused with the neurocranium dorsal to the vena jugularis, 

 which would be in marked exception to the conditions found in 

 all other fishes that I know of (Allis, 1915). It accordingly 

 seems to me, as above stated, that this shelf must represent 

 the extrabranchial of the arch, or processus oticus quadrati, 

 apparently found only partially fused with the palatoquadrate in 

 Dean's six-month embryo. The vena jugularis, ramus hyoideo- 

 mandibularis facialis, and arteria, carotis externa would then all 

 lie ventral and internal to this element of the arch, as they 

 normally should, and the foramina for these several structures 

 would represent the trigemino-facialis chamber of the fish, as 

 I have already suggested in an earlier work (Allis, 1914). 



The orbit has postorbital and antorbital processes. The 

 postorbital process is a pronounced and slightly curved ridge 

 which is fused ventrally with the suborbital shelf. The dorso- 

 lateral antorbital process is a short but tall ridge which lies at 

 the dorso-anterior edge of the orbit, and its base is perforated 

 by a foramen which transmits the ramus ophthalmicus super- 

 ficial trigemini from the orbit to the ethmoidal canal. 

 Immediately ventral to this process there is a foramen which 

 transmits a vein and artery, and antero-ventral to this latter 

 foramen there is another foramen which transmits the nervus 

 ophthalmicus profundus; both these foramina leading into the 

 median ethmoidal canal. A small foramen dorsal to these 

 foramina also leads into the ethmoidal canal and gives exit to 

 a small branch of the ophthalmicus superficialis. A small 

 foramen on the clorso-mesial surface of the nasal capsule gives 

 passage to a branch of the orbital branch of the external carotid, 

 and anterior to it there is another small foramen for a delicate 

 branch of the ophthalmicus nerve. The ventro-lateral antorbital 

 process is simply a ridge which traverses the suborbital shelf 

 and is continued onto the palatoquadrate, where it turns 



