268 THE CRANIAL NERVES. 



the rima glottidis, and a connecting filament which joins the long branch of the 

 upper laryngeal nerve beneath the hinder part of the thyroid cartilage : through this 

 communication sensory fibres are probably conveyed to the inferior laryngeal 

 nerve. 1 



The recurrent nei've also furnishes branches to the cardiac plexus, and twigs of 

 communication with the inferior cervical ganglion of the sympathetic, as it turns 

 round the large artery ; tracheal and oesophageal branches as it ascends in the neck ; 

 and lastly, offsets to the inferior constrictor of the pharynx as it passes beneath that 

 muscle. 



Varieties. In cases of dorsal origin of the right subclavian artery the inferior laryn- 

 geal nerve does not turn round that vessel, but passes inwards more directly to the larynx (see 

 Vol. II, p. 386). This nerve has been seen furnishing twigs to the crico-thyroid muscle. 



Cardiac branches. Branches to the heart are given off by the pneumo-gastric 

 nerve both in the neck and in the thorax. 



The cervical cardiac branches arise at both the upper and the lower part of the 

 neck. The upper branches, one or t\vo, are small, and join the cardiac nerves of the 

 sympathetic. The lower, a single branch, arises as the pneumo-gastric nerve is about 

 to enter the chest. On. the right side this branch lies by the side of the innominate 

 artery, and joins one of the cardiac nerves destined for the deep cardiac plexus : it 

 gives some filaments to the coats of the aorta. The branch of the left side crosses 

 the arch of the aorta, and ends in the superficial cardiac plexus. 



The thoracic cardiac branches of the right side leave the trunk of the pneumo- 

 gastric as this nerve lies by the side of the trachea, and some are also derived from 

 the first part of the recurrent branch ; they pass inwards on the air-tube, and end 

 in the deep cardiac plexus. The corresponding branches of the left side usually 

 come entirely from the recurrent laryngeal nerve. 



The depressor nerve of the rabbit would appear to be represented in man in many cases by 

 a slender branch which arises from the vagus in common with or just below the superior laryn- 

 geal nerve, or perhaps has a double origin, and either descends to the cardiac plexus in con- 

 junction with the superior cardiac nerve of the sympathetic (seldom independently), or rejoins 

 the vagus trunk from 1 to 3 cm. below its origin. In cases where this branch is not to be re- 

 cognised the fibres are probably contained in the vagus trunk as far as the lower part of the 

 neck. It is thought by Finkelstein and Alpiger that depressor fibres run in the cardiac offset 

 of the external laryngeal nerve. (A. Kreidmann, i; Anatomische Untersuchungen liber den 

 Nervus depressor beim Menschen und Hunde," Arch. f. Anat.. 1878 ; A. Finkelstein. " Der 

 Nervus depressor beim Menschen. Kaninchen, Hunde," &c., Arch. f. Anat., 1880 ; A. Viti. ' Re- 

 cherches de morphologic sur le nerf depresseur chez 1'homme et chez les autres mammiferes," 

 Arch. ital. de Biol., v, 1884 ; G. Bekesy. " Beitrage zur Anatomie der Herznerven," 1888 ; 

 M. Alpiger, ' ; Anatomische Studie liber das gegenseitige Verhalten der Vagus- und Sympathi- 

 cusaste im G-ebiete des Kehlkopfes," Langenbeck's Archiv, xl, 1890.) 



Pulmonary branches. Two sets of pulmonary branches are distributed from 

 the pneumo-gastric nerve to the lung ; and they reach the root of the lung, one on 

 its fore part, the other on its posterior aspect. The anterior pulmonary nerves, two 

 or three in number, are of small size. They join with filaments of the sympathetic 

 ramifying on the pulmonary artery, and with these nerves constitute the anterior 

 pulmonary plexus. Behind the root of the lung the pneumo-gastric nerve becomes 

 flattened, and gives several branches of much larger size than the anterior branches, 

 which, with filaments derived from the second, third, and fourth thoracic ganglia of 

 the sympathetic, form the posterior pulmonary plexus. Offsets from this plexus 



1 Howell and Huber, " Physiology of the communicating branch between the superior and the 

 inferior laryngeal nerves," Journ. of Physiology, xii, 1891. 



