426 



ZOOLOGY 



SECT. 



and cut off from the exterior, in the unmacerated skull, by the 

 tympanic membrane, are extremely small bones, which form a 

 chain extending, like the columella amis of the Pigeon, from the 

 tympanic membrane externally to the fenestra ovalis internally. 

 There are three of these auditory ossicles the stapes, which corre- 

 sponds to the columella of the Pigeon ; the incus, and the malleus, 

 with a slender process the processes gracilis. In addition there 

 is a small disk-like bone, the orlricular, which is attached to the 

 incus. 



The elements of the pectoral arch (Fig. 1020) are fewer than in 

 the Lizard. There is a broad thin triangular scapula, the base 



or vertebral edge of which has 

 a thin strip of cartilage (the 

 supra-scapular cartilage) con- 

 tinuous with it. Along the 

 outer surface runs a ridge 

 the spine; the spine ends 

 below in a long process the 

 acromion process (a.) - - from 

 which a branch process or 

 mctacromion (ma.) is given off 

 behind. The part of the 

 outer surface of the scapula 

 in front of the spine is the 

 pre-spinoiitS or pre-scapular 

 fossa (af.), the part behind the 

 post-spinous or post-scapular 

 fossa (pf.}. At the narrow lower 

 end of the scapula is a con- 

 cave surface the glenoid 



cavity- -into which the head of the humerus fits, and imme- 

 diately in front of this is a small inwardly curved process the 

 coracoid process (c.) which is represented by two separate ossi- 

 fications in the young Rabbit. A slender rod the clavicle 





 (cl.) is connected with the acromion process externally and 



with the sternum internally by means of fibrous tissue. At- 

 tached to the outer end of the clavicle is a small cartilage, 

 the meso-scapula (mss.) t and connected with its inner extremity 

 are two similar cartilages, which are supposed to represent the 

 ventral portion of the procoracoid (pc^) and the cpisternum of 

 the Sauropsidu. 



The skeleton of the fore-limb is more readily comparable with 

 that of the Lizard than with that of the Bird ; but there is a 

 difference in the position of the parts owing to the rotation back- 

 wards of the distal end of the humerus, all the segments being 

 thus brought into a plane nearly parallel with the median vertical 

 plane of the body, with the pre-axial border directed outwards, and 

 the original dorsal surface backwards. The radius and ulna are 



ps 



FIG. 1020. Lepus CUniculus. Shoulder- 

 girdle with anterior end of sternum of young 

 specimen. ". acromion ; (if. pre-scapular 

 fossa ; c. coracoid ; d. ossified clavicle ; ma. 

 metacromion ; mss. meso-scapular segment ; 

 ost. pro-sternum ; pc. pre-coracoid ; pf. post- 

 scapular fossa ; sr. sternal ribs. (After 

 Flower.) 



