442 ZOOLOGY SEC*. 



from which a branch process or metacromion is given off behind. 

 The part of the outer surface of the scapula in front of the spine 

 is the pre-spinous or pre-scapular fossa, the part behind is the 

 post-spinous or post-scapular fossa. At the narrow lower end of 

 the scapula is a concave surface the glenoid cavity into which 

 the head of the humerus fits, and immediately in front of this is 

 a small inwardly curved process the coracoid process which is 

 represented by two separate ossifications in the young Rabbit. 

 A slender rod the clavicle lies obliquely in the region between 

 the pre-sternum and the scapula, but only extends a part of the 

 distance between the two bones, and in the adult is only connected 

 with them through the intermediation of fibrous tissue. 



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 fixed in the position of pronation, i.e., the distal end of the radius 

 is rotated inwards, so that, while the proximal end is external to 

 the ulna, the distal end becomes internal, and the digits of the 

 manus are directed forwards. 



At the proximal end of the humerus are to be recognised : 

 (1) a rounded head for articulation with the glenoid cavity of 

 the scapula ; (2) externally a greater and (3) internally a lesser 

 tuberosity for the insertion of muscles ; (4) a groove, the bicipital 

 groove, between the two tuberosities. On the anterior surface 

 of the proximal portion of the shaft is a slight ridge, the deltoid 

 ridge. At the distal end are two articular surfaceSj one large and 

 pulley-like trochlea for the ulna ; the other smaller capitellum 

 for the radius : laterally are two prominences or condyles, an 

 internal and an external. 



The radius and ulna are firmly fixed together so as to be in- 

 capable of movement, but are not actually ankylosed. The radius 

 articulates proximally with the humerus, distally with the scaphoid 

 . and lunar bones of the carpus. The ulna presents on the anterior 

 aspect of its proximal end a deep fossa, the greater sigmoid cavity, 

 for the trochlea of the humerus ; the prominent process on the 

 proximal side of this is the olecranon process. Distally it articulates 

 with the cuneiform. 



The carpal bones (Fig. 1095), nine in number, are all small 

 bones of irregular shape. Eight of these are arranged in two 

 rows a proximal and a distal ; the ninth, centrale (cent.), lies 

 between the two rows. The bones of the proximal row are 

 taken in order from the inner to the outer side scaphoid (sc.), 

 lunar (or semi-lunar) (lun.), cuneiform (cun.), and pisiform. Those 



