176 DE. J. MUEIE ON THE FORM AND STEUCTUEE OF THE MANATEE. 



scapular region, where an artery (transverse humeral) of small calibre strikes directly 

 outwards, and terminally subdivides into a broad radiate rete mirabile, covering the 

 subscapularis, supraspinatus, &c. The single arterial tube is superficial to the cervical 

 nerves, but is itself enwrapped by portion of the vascular neck-plexus. Beyond and on 

 a level with the cricoid is a division apparently eqviivalent to internal and external 

 carotids. The former dips in among the rete mirabile at the posterior base of the skull 

 just behind the cranial series of plexuses. Among others, one occupies the poste- 

 rior portion of the great fissure between the occipital and tympano-periotic bones; 

 and whilst mingling with the cervical and spinal rete, complex branches are lodged 

 within the skull at what corresponds to a groove or recess of the lateral sinus, where 

 also venous channels obtain. The external carotid at the stylo-hyal and under cover of 

 the digastric and parotid gland bifurcates ; and jjlexuses are derived from both of these. 

 The branch agreeing with the facial runs towards the angle of the mandible and at the 

 concavity of the body of the bone turns upwards and is distributed with a plexiform 

 arrangement on the face. From its proximal end, and in fact enwrapping it, are retia, 

 which may be regarded as submaxillary, submental, &c. subdivisions ; and these lie 

 within the concavity of the jaw, twigs supplying the muscles and other parts, while 

 some inosculate with their fellows of the opposite side. The other, widest branch of 

 the external carotid ascends behind the mandibular angle, previously supplying plexi 

 to the parotid gland, superficies of the digastric, Sec. Other plexi, which were not 

 followed in detail, spread over the tympanic, temporal, and malar areas. At the ptery- 

 goid region there is separation of the external carotid into several thick retial bundles, 

 whereof the inferior dental, lingual, and internal maxillary are most conspicuous by 

 their volume. The vascular network, as it pierces the large vacuity of the lower jaw, has 

 a remarkably open character, resembling a mesh work of fibrous tissue ; and, as in Cetacea, 

 the interstices are partially occupied by fatty tissue and nerves. This vasculo-nervous 

 mass issues at the mental foramen, and supplies the lower labial parts. The numerous 

 capillaries of the internal maxillary division pass on to the pterygo-maxillary fissure, 

 and send inwards superior dental arterioles ; whilst the main mass, lying in the lateral 

 groove of the maxilla, is continued on through the orbit and emerges at the infraorbital 

 foramen, spreading amongst the fleshy and other structures of the face and snout. 

 Ciliary branchlets from the above are given off" to the eye &c. 



Stannius says that the subclavian artery divides into two main branches — a de- 

 scending large internal mammary, and the axillary. Before these divide, a very short 

 twig is sent upwards over the head of the first rib. Both arteries are equally split up 

 into narrow channels, which intertwine among the rete miiabile of the cervical region 

 and thorax. Von Baer likewise shows that the axillary artery becomes broken up into 

 minute vessels which overlie and are partly distributed to the shoulder and partly 

 continued on to the anterior extremity, mingling like the last with the rete cervicale. 



This is certainly the case, and the complexity and quantity of parallel channels is 



