100 The Pectoral Group of Muscles. [Dec. 6, 



2. That the radial division is of primary importance is shown by 

 the fact that each of these segments has its own nerve, viz., the 

 anterior, a nerve corresponding to external anterior thoracic of human 

 anatomy ; the middle, internal anterior thoracic ; the posterior, lateral 

 thoracic. The first is definite in its origin and distribution, and the 

 third in its origin, the second is less regular, and in correspondence 

 with this is a certain indefiniteness of the line of division between the 

 second and third segments. 



3. The anterior segment *may be subdivided into clavicular or 

 manubrial portions, and the posterior may also be in two divisions, 

 but these are not regarded as of primary value. 



4. Each segment may undergo a secondary lamination into super- 

 ficial and deep parts, viz,, anterior into superficial and deep manu- 

 brial, middle into gladiolar and costal, and posterior into superficial 

 and deep abdominal. 



5. Superficial manubrial is always present and generally covers the 

 others at its expanded insertion ; it may be distinct or fused with 

 deep manubrial or gladiolar, or both. 



6. Deep manubrial may be absent, or present and distinct, or fused 

 with, or just separable from, superficial. It may be fused with costal 

 or very rarely with gladiolar, if the plane of manubrial lamination is 

 more superficial than usual. The relation of this muscle to the so- 

 called " sterno-scapularis " is discussed, the author being of opinion 

 that the latter is subclavian in its nature. 



7. Gladiolar may be absent or nearly so. It may be distinct or fused 

 with superficial or deep manubrial, or with costal or abdominal. It 

 is very often fused at its posterior border only with costal, the two 

 sheets being otherwise separate. 



8. Costal may arise from the edge of the sternum and the costal 

 cartilages, from the cartilages alone, or from the ribs. It has a 

 tendency as it decreases in size to shift its origin farther outwards, 

 and its insertion farther towards the shoulder. It may be fused 

 with gladiolar or deep manubrial or abdominal. It may consist of 

 two portions, anterior and posterior. 



9. Abdominal may be absent or double, and the two parts may 

 overlie one another, or one may be anterior to the other. It may be 

 fused with gladiolar or costal. It may be connected by its entire 

 outer border with the dorsal sheet, thus closing the axilla, or fasciculi 

 may pass from one side to the other (achselbogen). The origin may 

 wander outwards to the lower ribs (pectoralis quartus). 



10. The parts above described are very variously arranged 

 amongst mammalia. The conditions obtaining are discussed and 

 exhibited in a tabular form. 



11. The various factors are thus represented in man : 



