8o Anatomy of Skeleton 



Enough has been said already to show that the body can be recognised as the dorsal portion or 

 scapular part of the girdle, while the coracoid belongs to the ventral division. But which of the 

 two ventral bars is represented by it is not at all clear. If it is the caudal element, then the pre- 

 coracoid has either disappeared, or has been partly taken up in the clavicle, and partly remains 

 outside this as fibro-cartilage, etc. If it is really precoracoid, the true coracoid has disappeared, 

 or may be represented by the supraglenoid centre : this last view accords with ossification periods, 

 but leaves the cartilage in and around the clavicle unaccounted for. Those that have a fancy for 

 homologising the two girdles can compare the coracoid process with either the pubis or ischium, 

 according to the view they take of the value of the process. 



Following the process of its development, it seems that the spine ought to be considered merely 

 a muscular process, except perhaps as concerns its thick outer margin, which is preformed in car- 

 tilage : it is possible that this may have to be considered in the future as representing a ventral bar 

 much modified. The ventral surface of the scapula has been homologised with the gluteal surface 

 of the Ilium, on the assumption that rotation of the girdles has altered their disposition ; there 

 seems to be no ground for this assumption. 



HUMERUS, 



A long bone forming the skeleton of the upper arm, articulating with the scapula 

 above and with the bones of the forearm below : it has an elongated shaft with expanded 

 upper and lower ends (Fig. 61) . The upper end has an articular head directed upwards, 

 inwards and very slightly backwards, joined to the rest of the bone by a slightly con- 

 stricted anatomical neck. The remainder of the upper end presents in front a small 

 tuberosity for insertion of Subscapularis, separated by a deep bicipital groove (for long 

 tendon of Biceps) from the larger mass of the great tuberosity : this has upper, outer, 

 front, and back aspects, being continuous with the bone on its inner aspect, and has 

 three quadrilateral facets on its upper and back aspects for the tendons of Supraspinatus, 

 Infraspinatus, and Teres minor. 



The upper end joins the shaft by the surgical neck, a common site of fracture 

 spoken of by surgeons as " fracture of the neck " of the bone. The shaft : front 

 surface has, at the upper part, the continuation of the bicipital groove, bounded by 

 inner and outer lips, continuous with small and front part of great tuberosity respec- 

 tively : inner lip has a rough marking for Teres major, and outer lip has insertion of 

 Pectoralis major while the floor of the groove gives attachment to Latissimus dorsi at 

 a somewhat higher level. The outer lip runs down into the front part of a rough 

 deltoid impression which is on the outer side of shaft. Nearly opposite this on the 

 inner side, but as a rule a little lower, is the slight impression for Coraco-brachialis. 



Upper half of shaft is more or less cylindrical, but the lower half widens to carry 

 the lower end, so that the posterior surface is flattened in the lower part but rounded 

 above : about half-way down, near the outer side behind, a slight twist in the bone 

 gives the appearance of a badly-defined groove, the musculo-spiral groove, which passes 

 spirally downwards towards a point a little distance below the deltoid impression : 

 it has the musculo-spiral nerve and superior profunda artery in relation with it. The 

 outer head of Triceps arises above and outside the groove, and the large inner head 

 below and internal to it. The front surface of the lower half is not flattened, but 

 presents a rounded, broad anterior border or ridge dividing it into antero-internal and 

 antero- external surfaces : the ridge is continuous with the external lip of the groove 

 above. This front surface of the lower part of the shaft gives origin to the Brachialis 

 anticus which covers it, and is bounded at the sides by internal and 'external supra- 

 condylar ridges which lead down to the internal and external condyles. 



The external supracondylar ridge has the outer intermuscular septum attached to 



