-2 1 8 FISHES CHAP. 



certainty the component parts as being represented in other 

 Craniates. On each side of the cranium, beneath the eye, there is 

 a characteristic V-shaped subocular arcli. Of its two legs the 

 hinder one is continuous above with the periotic region of the 

 cranium, and the other with the anterior trabecular region, while 

 the pointed apex is directed obliquely downward and forward. 

 From the hinder margin of the posterior limb a slender styloid, 

 process passes downward in the side wall of the pharynx, and 

 terminates below in a forwardly directed cornual cartilage. A 

 velum, fringed along its free margin with a series of tentacles, 

 projects forwards into the oral cavity from between the oral 

 apertures of the oesophagus and the branchial canal, and probably 

 serves to prevent the entrance of foreign particles to the gill-sacs. 

 This valve-like velum is supported by a velar skeleton, consisting 

 of two lateral cartilages which are prolonged into the tentacles, 

 and extend transversely between the inner surfaces of the two 

 styloid processes. The apex of each subocular arch is connected 

 with a small and somewhat triangular cartilage (postero-lateral 

 cartilage), which is directed upward and forward, and lies in the 

 side wall of the oral cavity. With some degree of probability 

 the subocular arch may be compared to the palato-quadrate 

 cartilage of a skull which has become " autostylic " in order to 

 form a rigid support for the skeleton of the buccal funnel ; 

 the styloid processes and cornual cartilages to the hyoid arch ; 

 while the relations of the posterior lateral cartilages to the sub- 

 ocular arches suggest that they may possibly be regarded as 

 Meckelian cartilages which have lost their primitive function of 

 forming biting jaws. In the median line below, and projecting 

 backward for some distance beneath the branchial canal, there is 

 a long and stout lingual cartilage, carrying a small median and a 

 still smaller pair of lateral cartilages at its anterior extremity, 

 where it supports the lingual teeth and projects into the buccal 

 funnel beneath the mouth. In front of the lingual cartilage, 

 and connected by fibrous tissue with the inferior and hinder 

 margin of the annular cartilage, there is a median T-shaped 

 element, the median ventral cartilage. It has been conjectured 

 that the lingual cartilage is a free basi-hyal element, and the 

 median ventral cartilage the equivalent, elsewhere unknown, of 

 the corresponding element of the mandibular arch.^ 



^ Huxley, op. cit. p. 421. 



