5G8 



ANATOMY OF VERTEBRATES. 



440 



fied, only the peripheral row was visible, the rest of the mass 

 being opaque. In terrestrial Insectivora the thymus is less 

 ambiguous, and consists of two nearly equal lobes lying on the 



base of the heart and 

 beginnings of the great 

 vessels. In the Hedge- 

 hog were found ' two 

 roundish masses almost 

 precisely similar to 

 those in the same situ- 

 ation in the Bat, and 

 two broader and thin- 

 celloid particles were 

 and in some parts they 

 oily matter diffused in 



Convexity of lobe of cervical tliymus-like body, Bat. xcxiv' 



ner 



ones lying in the axilla.' 1 * The 

 more loaded with oil than in the Bat, 

 were more or less broken up and the 

 the cavity.' 2 In both cases these lobulated masses may be well- 

 marked modifications of the adipose tissue. In Cetacea a thymus 

 has been recognised in Balana mysticetus, the right lobe ex- 

 tending over the aortic arch to the trachea, where it terminates 

 in two small cornua, the left lobe being of smaller size. ' In the 

 foetal Dolphin these are two large median portions, pericardiac 

 and tracheal, with deep-seated lateral cornua.' 3 In a foetal 

 Elephant the thymus is a flat mass beneath the anterior part of 

 the pericardium, with a short forward prolongation of the right 

 lobe. In the Rhinoceros the thymus holds a like position, and 

 encroaches but a little way upon the neck. In the Artiodactyles, 

 whether ruminant (Ox, Deer) or non-ruminant (Peccari), the 

 cervical portions of the thymus are more developed, often ex- 

 tending to the mandibular angles. The thymus of the Calf is 

 very large and affords a good subject for investigating the struc- 

 ture of this body. In Carnivova the thymus has the usual posi- 

 tion in the thorax, to which it is limited ; it soon shrinks, and in 

 Felines disappears. At its fullest phase of development in the 

 Cat, the thymus is thick from before backward, and its right and 

 left lobes closely interdigitate. In a young Seal, Simon found it 

 in two symmetrical, broad, thickish lobes, extending to the root 

 of the neck, and f abruptly terminated by clubbed extremities, 

 which are deeply grooved in front by the left vena innominata.' 4 

 In most Quadrumana, especially the Catarhine group, the 

 thymus presents the same general shape and relations as in the 

 human subject. 



§ 253. Adrenals. — These bodies are best developed in Mam-? 



1 ccxiv". p. 1096. 2 lb. » ccxv". 4 lb. 



