THE THORACIC RETE 



335 



capitis anticus major (e), leaving only a small slit, widening caudally, between itself 

 and that muscle. In front, therefore, of the thorax the scalene forms a large part of 



the ventral boundary of the rete as well as the 

 rectus. Through the slit the rete protrudes, so 

 as to come into brief contact with the subcla- 

 vian artery (g) and the sterno-mastoid muscle 

 (di). 



The shape of the thoracic cavity is peculiar in 

 the Cetacea. The diaphragm is very obliquely 

 set and the ventral line of the cavity is far 

 longer than the dorsal. The thorax projects 

 far forward on each side in front of the heart 

 and the great vessels, so that two domes 

 of the thoracic cavity — the pleural domes — 

 extend forward above the subclavian arteries 

 nearly to the posterior face of the first rib. 

 The forward extension of the dome is re- 

 presented by the dotted line above mentioned 

 on the right side of Fig. i. The caudal aspect 

 of the pyramidal retial mass — the posterior 

 side of the triangle — lies very close against this 

 forward extension of the thorax underneath 

 the pleural lining. It is therefore markedly 

 concave in outline. It overlies the whole of the 

 first intercostal area and the proximal third of 

 the second, lying between the pleuron and the 

 intercostal muscle. 



The main body of the retial mass occupies 

 the length of the vertebral column from the 

 i st cervical to the 4th dorsal vertebra and has 

 the relations to the vertebrae already outlined. 

 Between the 1 st and 2nd cervical vertebrae there 

 is a large lobe of the retial substance which com- 

 municates with the main body of the rete only 

 by a neck passing through the foramen of the 

 transverse process of the 2nd cervical vertebra. 

 This portion is in relation laterally with the 

 splenial and trachelo-mastoid muscle complex, 

 and not with the scalene, which has passed me- 

 sially to its insertion upon the basis cranii. Pos- 

 teriorly, between the transverse process of the 

 4th and 5th and the 5th and 6th dorsal vertebrae , 



Fig. 2. Diagrammatic transverse section through 

 the base of the neck, showing the main mass of 

 the Rete (dotted) and its relation to the muscles 

 and the vertebral column. 



a, Semispinalis muscle 



b, Longissimus dorsi muscle 



c, Scalene muscle 



d 1, Sterno-mastoid muscle 



d 2, Sterno-mandibularis muscle 



e, Rectus capitis anticus major muscle 



/, Longus colli muscle 



g, Subclavian artery 



h, Brachiocephalic vein 



i, Posterior thoracic artery 



j, Posterior thoracic vein 



k, Intraspinous vein 



/, Neural sinus 



m, Ascending artery 



n, Trachea and oesophagus 



