TONGUE OF VERTEBRATA. 



553 



food. In many Prosimii and Chiroptera, as also in the platyrrhine 

 Apes, there is a process below the tongue which is sometimes 

 double; this is the so-called subliugua. 

 The glandular organs connected 

 with the buccal cavity are developed 

 from its mucous membrane. When 

 they are largely developed, and are 

 placed outside the mucous membrane, 

 their efferent ducts pass into it. 

 They may therefore be regarded as 

 greatly developed glands of the mucous 

 membrane. Larger glands of this kind 

 are placed between the nasal capsules, 

 and on the palate, in the Amphibia. 

 When they are much larger they may 

 extend on to the skull (intermaxillary 

 glands). The labial glands, which are 

 set along the edges of the jaws in the 

 Reptilia, must be mentioned (Ophidii 

 and Saurii). The poison-gland of the 

 Ophidii is a larger organ, but is merely 

 formed by a modification of simple 

 glands. In the Chelonii there is a 

 pair of glands below the tongue, which 

 are regarded as salivary glands. The 

 Saurii also are provided with similar 

 groups of separate glands. Larger 

 glands of this kind, which aid in the 



production of a buccal fluid, are also found in different regions. 

 They are constant in Birds and Mammals, and are distinguished 

 as sub -maxillary, sublingual, and parotid glands. In Birds the last 

 of these open at the angle of the mouth, but in Mammals, in the 

 vestibulum oris. These glands 

 are not developed in the Cetacea, 

 and but feebly in the Pinnipedia. 

 The three pairs are largest in 

 Herbivora; sometimes one and 

 sometimes another pair being the 

 best developed. 



Fig. 310. Hyoid apparatus, with the 

 tongue and trachea of Varauus. 

 e Median piece of the hyoid. 

 h' Anterior, h" Posterior cornu 

 of the hyoid. m m' Muscles. 

 tr Trachea. % Tongue. 



§ 416. 



Fig. 311. Sections through the body of 



young larvaa of Petromyzon to show the 



ventral groove, d Branchial cavity (after 



Calberla). 



Mention has still to be made 

 of the hypobranchial groove 

 and its derivates. It is an organ 



differentiated from the primitive cephalic enteron (cf. p. 540). In 

 Amphioxus it extends all along the branchial cavity. Among the 

 Cyclostomata it has only been observed during the early larval con- 

 dition of Petromyzon (Pig. 30 i, //). As it does not extend along 



