102 THE STRUCTUKE OF MAN 



upon as forward extensions of the same. The neck, as has been 

 seen from the study of the skeletal system (ante, p. 43), was 

 formerly provided with free ribs ; and hence this serial relation- 

 ship of the cervical to the segmental thoracic muscles is easily 

 understood. The degeneration of the cervical ribs has had 

 (among other results) the effect of causing the short-fibred scaleni 

 muscles, which once only stretched across the intercostal spaces, 

 to unite and grow longer, so as finally to reach ribs which lie 

 farther back. Further related modifications may be exemplified 

 in the occurrence of supernumerary scaleni, such as the scalenus 

 minimus (scalene intermediaire, Testut), which is typically present 

 in all Anthropoids, and by the numerous variations in origin and 

 attachment of the three ordinary scaleni. 



The transversus thoracis muscle (triangularis sterni) is clearly 

 degenerating. This muscle, which lies on the inner side of the 

 anterior wall of the thorax, arises from a variable number of slips. 

 It arises, as a rule, from the cartilages of the third to the sixth 

 ribs, and occasionally receives a slip from the seventh rib also. 

 This fact helps us in homologising it as a continuation of the 

 transversalis abdorninis. These two muscles are separated by one 

 of the bundles which give rise to the diaphragm. 



THE MUSCLES OF THE CERVICAL AND CEPHALIC EEGIONS 



In addition to the structural changes going 011 in the scaleni, 

 which have been already mentioned, the following facts are worth 

 recording : 



The original community of the trapezius and the sterno- 

 cleido-mastoid muscles is indicated by their common innervation, 

 and further by the fact that the interval between them is still 

 not infrequently occupied by the cleido-occipitalis which runs 

 from the clavicle to the occipital bone. This muscle thus forms 

 a link between the trapezius and the sterno-cleido-mastoid, 

 and when strongly developed brings about a more or less 

 complete fusion of these two muscles, i.e. reinstates the original 

 condition. 



These facts might have been included in the remarks on 

 muscles which occasionally appear and may be considered atavistic, 

 but they are here dealt with as they indicate a gradual dis- 

 appearance of certain fibrous areas in the region of these muscles, 

 i.e. they point to a retrogressive condition. 



A similar relationship exists between the anterior belly of 



