CIRCULATION IN SPECIAL PARTS. 141 



on mere exposure of the veins. The skeletal muscles, and especially 

 the abdominal respiratory muscles, act as a tonic mechanism to the 

 veins. Thus the abdominal wall is of the utmost importance, in so far 

 as it tonically maintains the calibre of the great abdominal veins, and 

 can at any moment compress these vessels or allow them to expand. 1 



CIRCULATION" IN SPECIAL PARTS. 

 The Cikculation in the Head. 



Vasomotors of face and mouth. — The vaso-constrictor fibres for 

 the head issue by the upper thoracic anterior roots (1 to 5 in the dog), 

 and pass into the cervical sympathetic nerve. 2 



The vaso-dilator supply to the face and mouth has been investigated 

 by Dastre and Morat. 3 These fibres issue also from the upper thoracic 

 roots, and pass up the cervical sympathetic nerve to the Gasserian 

 ganglion, and thence to the fifth nerve. Some of the dilator fibres 

 issue directly from the cranial origin of the fifth nerve, for stimulation 

 of this nerve between the pons and the Gasserian ganglion causes Hush- 

 ing of the face. Excitation of the lingual and glosso-pharyngeal nerves 

 dilates the vessels of the tongue, while stimulation of the hypoglossal 

 nerve causes them to contract. These constrictor fibres come from the 

 superior cervical ganglion. 



The circulation in the mucous membrane of the mouth has been 

 examined by direct observation, while the volume of the tongue can be 

 investigated with a suitable plethysmography By observing the effects 

 of section or excitation of the cervical and thoracic sympathetic nerve, 

 during ophthalmoscopic examination of the eye in the curarised rabbit, 

 both vaso-constrictor and vaso-dilator nerves have been found to pass to 

 this organ. 5 



Vasomotors of salivary glands. — The vaso-constrictor fibres to the 

 submaxillary gland issue from the first and second, or the second and 

 third, thoracic anterior roots, and pass up the cervical sympathetic nerve. 

 The cell stations for these fibres lie in the superior cervical ganglion. 6 



The vaso-dilator fibres to the submaxillary gland pass by way of the 

 chorda tympani from the facial nerve, and have their cell stations in 

 contiguity with the gland. The vaso-dilator fibres to the parotid gland 

 issue from the glosso-pharyngeal nerve, and pass to the gland by way 

 of the auriculo-temporal nerve (see vol. i. p. 482). The circulation in 

 these glands has been studied by placing a cannula in an efferent vein 

 and observing the outflow, or by exposing the gland and directly inspect- 

 ing its colour. 



Cerebral circulation. — Observations on the movements of the brain 

 are to be found recorded in the earliest medical writings. Whenever 

 the brain is exposed by defects in the wall of the cranium, the brain 

 can be seen to pulsate. This phenomenon can be demonstrated with 



1 Hill and Barnard, Joum. Physiol., Cambridge and London, 1897, vol. xxi. p. 323. 



2 Claude Bernard, Joum. de la physiol. de Vhomme, Paris, 1862, tome v. p. 413 ; 

 Dastre and Morat, " Recherches sur le syst. nerv. vaso-moteur, " Paris, 1884, p. 325; 

 Langley, Phil. Trans., London, 1892, vol. clxxxiii. p. 85. 



3 Loc. cit., p. 115 et seq. 



4 Piotrowski, Centralbl. f. Physiol., Leipzig u. Wien, 1887, S. 454. 



5 Morat and Doyan, Arch, de physiol. norm, et path., Paris, 1892, p. 60, cf. v. 

 Schulten, Arch. f. Ophth., Leipzig, 1884 (4), Bd. xxx. S. 65. 



6 Langley, Phil. Trans., London, 1892, vol. clxxxiii. p. 97 ; Joum. Physiol., Cambridge 

 and London, 1890, vol. xi. p. 123. 



