72 PROFESSOR DAVID HEPBURN ON 



formed a diarthrodial joint. On the ninth costal cartilage this muscle interdigitated 

 with the attachment of the diaphragm. This large, well-developed muscle was supplied 

 by a series of twigs derived from the intercostal nerves in relation to which it was 

 attached. 



The sterno-mastoid muscle extended from the anterior end of the sternum and from 

 the side of its pointed suprasternal cartilage to the mastoid process. There being no 

 clavicle, this muscle appeared narrow. 



The sterno-hyoid and sterno-thyroid muscles arose from the sternum under cover of 

 the previous muscle. They formed a thin continuous sheet which probably included 

 the omo-hyoid muscle along its lateral border in the vicinity of the hyoid bone. The 

 entire sheet was innervated from the hypoglossal nerve, and the insertion of fibres into 

 the thyroid cartilage and into the hyoid bone suggested the character of its constituent 

 parts. A thin band of muscle fibres occupying their usual position formed the thyro- 

 hyoid muscle. 



There were two well-defined scalene muscles, both of which were situated on the 

 dorsal side of the subclavian vessels and cervical nerves, and may therefore be regarded 

 as the representatives of the scalenus medius and scalenus posticus muscles. 



The musculus scalenus medius was inserted into the costal cartilage of the first rib 

 close to the costo-chondral articulation. 



The musculus scalenus posticus was inserted into the lateral aspects of the third, 

 fourth, fifth, and sixth costal cartilages close to the costo-chondral articulations. At 

 each insertion the pointed attachment interdigitated with similar attachments of the 

 musculus obliquus externus abdominis, whose digitations extended to the cartilage of 

 the first rib. 



Regarding the skull and the cervical column as providing the more fixed or rigid 

 attachment for the -scalene and sterno-mastoid muscles, it is fairly evident that these 

 muscles may act as elevators of the ribs and sternum by drawing them towards the head. 



The diaphragm was well defined in all its parts, but its dorso-lateral portions were 

 very thin, and in the absence of a central tendon of the trefoil type it presented appear- 

 ances deserving detailed description, more especially in regard to the important position 

 occupied by this muscle in the mechanism of respiration. Its strongest part was the 

 mesial or vertebro-sternal element, which presented two well-marked, pointed crura 

 attached to the lumbar vertebrae. From this origin the muscular fibres passed in a 

 ventral direction on either side of the abdominal aorta until they reached the ventral 

 aspect of this vessel, where to a small extent their fibres intermingled ; but for the most 

 part the fibres of the right crus were on the ventral side of those of the left crus. 



This distinction between the fibres of the two crura was maintained as they continued 

 towards the oesophagus, along the lateral aspects of which they passed, thereby forming 

 the cesophageal opening, which was practically in the mesial plane. A short distance 

 on the ventral side of the oesophageal opening the muscular fibres were inserted into a 

 circular tendinous ring placed slightly to the right of the mesial plane, and through this 



(ROT. soc. EDIN. TRANS., VOL. XLVIII., 322.) 



