MAMMALS. 561 



somewhat concave, whilst the outer surface, on the contrary, is usu- 

 ally more or less convex. A projecting crest, named spine (spina 

 scapulae], generally divides this outer surface into two parts, and 

 extends upwards over the articular surface of the scapula. In the 

 cetaceous animals the spine lies close to the anterior margin of the 

 scapula, so that the anterior cavity (fossa supraspinata) is particu- 

 larly small. In the bats the scapula has some resemblance to that 

 of birds in its narrow and lengthened form. 



The upper-arm bone or humerus in man is nearly straight. In 

 the carnivorous animals, on the contrary, it is much bent, and its 

 articular head lies out of the axis. It is short in the ruminants 

 and the horse, where the extent of the forehand is great. Very 

 short is it especially in the cetaceans, long, on the other hand, in 

 the quadramanous mammals and the sloths. 



The humerus in many quadrumanous animals, in the genus 

 Felis, Mustela, in the squirrels, perhaps in all the edentates, with 

 the exception tf Bradypus tridactylus 1 , and in some other mammals, 

 is perforated above the elbow or provided with an oblique canal. 

 Through this canal or this aperture (foramen supracondyloideum) 

 there runs by no means, as was formerly asserted, the tendon of the 

 bicipital musele, but the median nerve of the arm and the brachial 

 artery or the ulnar artery, and often also the ulnar vein 2 . This 

 canal or passage is absent in all cetaceous and ungulate animals. 

 It must not be confounded with another aperture at the inferior 

 extremity of the humerus between the two condyles which is some- 

 times observed even in man, where the bone at this part is a thin 

 lamina. This aperture is particularly large in the daman and in 

 some rodents. 



With the inferior extremity of the humerus the two succeeding 

 bones of the fore-arm are connected by hinge-articulation. The 

 ulna is the longest of the two in man ; it lies on the inside of the 

 fore-arm and backwards. Its upper extremity has a deep articu- 

 lar surface (cavitas sigmoidea], and terminates behind in a hook 



1 See A. BRAXTS Diss. zool. inaug. de Tardigradis. L. B. 1828, 4to, pp. 42, 43. 



2 Thus it was observed first in the lion by WOLFF, and afterwards in the apes by 

 TIEDEMANN : see the paper of the last named in MECKEL'S Archiv fur die PTiysioL rv. 

 1818, s. 544 549. Comp. also V. BAER ibid. v. s. 312 314, and OTTO Comments- 

 tiv.ncula de rariorib. quibusd. sceleti humani cum animalium sceleto analoffiis. Vratis- 

 laviae, ^39, 4 to, pp. 25 -27. 



VOL. ii. 36 



