418 Bashford Dean Ivlemorial Volume 



(less than a millimeter). The finer structure of this specimen is rather poorly preser^-ed, 

 but permits of the foUo^^Tng obser\-ation5. The duct (d.) is lined u-ith stratified squamous 

 epithelium continuous -^-ith the epithelial lining of the phar^^nx. The outer layer of the 

 duct consists of a thick layer of dense connective tissue continuous v.'ith a similar layer 

 comprising the deeper portion of the mucous membrane of the pharynx. Between the 

 epithelium of the duct and its connective tissue layer, there are many calcifications ha\ing 

 the form of rudimentan,'- denticles. These are smaller than the fully developed denticles 

 (p.d.) that occur in the lining of the phar^^nx. The distal end of the duct ends blindly 

 in close contact with the th^Toid (thyr.). 



Text-figure 76 is a drawing of the thyroid of one of my specimens (No. Ill) in which 

 a th^TOglossal duct is absent. The histological condition of this material, also, is rather 

 poor, but the topographical relations are well shouTi. Upon comparing Text 'figures 76 

 and 75, it v,-ill be seen that in specimens I and III the position of the main mass of 

 the thyroid (thyr.) with respect to the large foramen in the basihyoid cartilage (c.) is not 

 quite the same. 



In specimen No. IV a large part of the th>Toid was cut av.^y in trimming the block 

 preparatory to imbedding, but in the remaining portion the finer structure is well presen.-- 

 ed. While the simple cuboidal epithelium of the follicles is in good condition, the lumens 

 of the foUicles appear empty, as they do in the other specimens. In the sections of Xo. 

 rV, the phar5.'ngeal denticles are beautifully sho-<;^-n. In all the sections, the epithelial 

 Lining of the phar^^nx is very poorly preser\'ed. Fundamentally, it is stratified epithelium, 

 but it contains many unusually large pale cells, singly or in groups, which are probably 

 mucous cells. 



In Heptanchus (Daniel, 1934, p. 123) the thyroid gland is located "'at the symphysis 

 of the lower jaws between the coracomandibularis and coracohyoideus muscles.'" FergU' 

 son (1911), after studying many species of elasmobranchs, states that "The [th>Toid] 

 gland rests upon the basihyal cartilage whose anterior margin forms an excellent guide 

 to its location." His paper deals with the histological structure as weU as the form and 

 gross anatomical relations of the thyroid in elasmobranchs, and includes a description of 

 the blood vessels supplying the th\Toid. In Scylliu-m catulus and in S. camcula f^Goodey, 

 1910.2), the th\Toid gland is situated close to a foramen in the basihyoid cartilage. In 

 both species of Scyllium the connective tissue investment of the th\Toid extends into 

 the foramen as a plug containing, in some instances, a small amount of th}Toid tissue, 

 and in one instance, a problematical duct. So far as our present knowledge extends, 

 Chlamydoselachus is the only vertebrate possessing, at least occasionally, a persistent 

 th>Toglossal duct. 



THE SPLEEN' 



In ChlamydoseJachus the spleen proper fText-figure 72, sp.l) is a very elongate, 

 somewhat comma-shaped, flattened organ lying in the dorsal mesenter)' at the level of 

 the pylorus, pyloric vestibule, and caudal end of the cardiac stomach. In its natural 



