186 THE VOYAGE OF H.M.S. CHALLENGER. 



PLATE IX.— The Thoracic Viscera of TIIYLACINUS, and the 



Feet of various Mammals. 



Fig. 1. The heart and lungs of Thijlacinus. 



a. Subclavian vein (right). 



b. Internal jugular vein (right). 



c. Right subclavian artery. 



d. Rig;ht common carotid artery. 



e. Left common carotid artery. 



f. Left subclavian artery. 



g. Left internal jugular vein. 

 h. Left subclavian vein. 



i. Superior intercostal vein. 



n. Left anterior vena cava. 



k. Posterior vena cava. 



m. Right anterior vena cava. 



I. Azygos vein. 

 Fig. 2. Dorsal aspect of the left foot of the Three-toed Sloth. 



fl.br.d. Extensor brevis digitorum. 



d 1 . First dorsal interosseus. 



d, 3 . Second dorsal interosseus. 



d\ Third dorsal interosseus. 



d\ Fourth dorsal interosseus. 

 Fig. 3. Palmar aspect of the left manus of the Three-toed Sloth. 



2 nd p. i. Second phalanx of the index. 



2 nd p.m. Second phalanx of the medius. 



2 nd p.a. Second phalanx of the annularis. 



p 2 *. Adductor indicis. 



p 2 . Transversus indicis. 



p*. Adductor annularis. 



f 1 . Flexor brevis pollicis. 



p.r. Radial head of flexor brevis indicis. 



f*. Flexor brevis annularis. 



f". Flexor brevis minimi digiti. 



d.u.n. Deep division of the ulnar nerve. 

 Fig. 4. The same manus with the adductors reflected (drawn somewhat larger than 

 nature). 



p. 2 Transversus indicis. 



