542 ANATOMY OF VERTEBRATES. 



the right side ; the spermatic arteries arise close together but sepa- 

 rately in the male vulpine Phalanger : k is the femoral artery ; I the 

 external, m the internal branch; i is the caudal artery, which 

 here corresponds in size with the development and functional im- 

 portance of the tail, and is very small in the tail-less or nearly tail- 

 less Marsupials, such as the Choeropus, Koala, and Wombat. 



The proportions in which the vertebral and entocarotid arteries 

 supply the brain continues to characterise the Lissencephala, and 

 relates rather to the restricted development of the cerebrum than 

 to any special proneness to hybernation or torpidity. The artery, 

 moreover, which, entering the basis cranii, represents the ento- 

 carotid, supplies parts usually served by the ectocarotid, in 

 Gyrencephala. Thus, in the Hedgehog, a branch of the carotid, 

 after sending off twigs to the occipital muscles, penetrates the 

 petrosal bulla, and there divides: one branch, traversing the 

 stapes, gives off the middle meningeal artery, and is continued 

 forward by the orbitosphenoid fissure into the orbit : the other 

 branch, truly representing the entocarotid, passes into the cranial 

 cavity, and joins the ' circle of Willis,' which is mainly formed by 

 the vertebral arteries. Evidence of this condition of cephalic 

 arteries in other Insectivora and in Rodentia is given in fig. 173, 

 c and E, as regards the passage of the petro-tympanic branch 

 through the arch of the stapes. In the Hare the division of the 

 carotid which sends off the entocarotid pierces the petro-tympanic 

 bulla, as in the Hedgehog : in the Capybara it grooves the basi- 

 sphenoid. In the Hedgehog each carotid gives off, near its 

 origin, the inferior thyroid : in the Anteater, the inferior thyroids 

 have a common origin from the innominate trunk. In most 

 Kodents which have the entocondyloid perforation of the humerus 

 (vol. ii. pp. 382-384) the brachial or ulnar artery accompanies 

 the median nerve through that hole : in Myrmecophaga the nerve 

 only so passes. In Bats the brachial bifurcates about the middle 

 of the humerus : the deeper-seated division supplies the extensors 

 of the fore-arm. 



The most remarkable modification of the brachial artery is 

 that which was discovered by Carlise, 1 in the Sloths and Slow- 

 lemur, and which is repeated in the femoral of the same ani- 

 mals. The divers interpretations, leading to controversy, on 

 these peculiarities of the arterial system in cxiv'', cxv", cxvi", 

 called for special care and attention to the subjects afforded to me 

 by the London Zoological Society, in respect to the arterial system. 



In the Ai (Brady pus tridactylus) the arch of the aorta, opposite 



1 CXLIIl". p. 17. 



