948 THE OSTEOLOGY AND MYOLOGY OF THE DEATH ADDER, 



stratum as it runs back towards the posterior extremity, we see 

 that true external intercostals are formed between the ribs. Of 

 these external intercostals those fibres which are nearest the 

 vertebrae begin first to alter their direction, so that we have formed 

 a series of levatores costarum externi, whose fibres are directed from 

 within, backwards, and outwards ; and since the layer reaches 

 through the whole depth of the intercostal space, we have the 

 internal fibres similarly aff'ected, and thus are produced the levatores 

 costarum interni. But not only do the fibres next the vertebrae 

 change, but also those which lie between the intercostal cartilages 

 change from the true external intercostal direction to a more 

 antero-posterior one. This is brought about by the cartilages of 

 the ribs bending forward. Thus are produced the " retrahentes 

 costarum breves " (Hofi*mann). We find the arrangement described 

 above on the first intercostal spaces ; but as we go more poste- 

 riorly we find, arising from the ribs at the place where the levatores 

 costarum interni are inserted, bundles of fibres which run outwards 

 and backwards over two or three ribs. These are the first pretra- 

 hentes costarum superiores ; and they are evidently formed by the 

 continuation of the fibres of the external intercostals over more 

 than one intercostal space. It is to be noted as supporting this, 

 that they spring from where the levatores are inserted, and that 

 where there are levatores there are no other muscles of this group 

 overlying them. As we follow these muscles back, we find that 

 the fibres cross more intercostal spaces until they reach their 

 maximum by being inserted into the ninth rib from the origin, at 

 the same time however they give slips to all the ribs crossed over. 

 Not only have we formed a group of pretrahentes costarum superi- 

 ores, but we have also an inferior group formed in the same manner, 

 the only difterence between the two being that the fibres of the 

 inferior group, since they arise at the junction of the inner two- 

 thirds with the outer third, must necessarily run more antero- 

 posteriorly than the superior group. 



Beside these intercostal muscles we have obliquus internus 

 proper, and also a rectus, with its modification in the scutal muscles 

 and the hyoid group. 



