CESOPHAGUS 251 



muscle fibers. These fibers are not a downward extension of the striated 

 pharyngeal constrictors, but apparently develop from exactly such mesen- 

 chymal cells as produce smooth muscle further down. The striated 

 muscles in man are limited to the upper half of the oesophagus ; in the rabbit 

 they extend its whole length. 



The adventitia is loose connective tissue, containing many vessels and 

 the plexiform branches of the vagus nerves. From these nerves, medul- 

 lated and non-medullated fibers enter the oesophagus and form a ganglion- 

 ated myenteric plexus between the muscle layers, and the plexus submu- 

 cosus in the submucosa. Medullated fibers proceed from the vagus 

 trunks to the motor end plates of the striated muscles, which are thus 

 stimulated reflexly from the central nervous system. Other fibers pass 

 from the myenteric plexus to the plexus submucosus and thence to the 

 epithelium, in which free nerve endings have been found. Such fibers, 

 together with those to the smooth muscles, provide for local reflex action, 

 whereby the contents of the oesophagus causes contraction above, and re- 

 laxation below, the place of stimulation. This takes place independently 

 of the central system, and is the form of innervation characteristic of the 

 intestine. 



STOMACH. 



Form and Subdivisions. The opening through which the oesophagus connects with 

 the stomach is the cardia (Gr. KapSui, heart), and the opening from the stomach to the 

 intestine is the pylorus (Gr. 7rvA.o>pds, gate-keeper). The pylorus received its appropri- 

 ate name from Galen (in the second century), who recognized that through its sphincter 

 muscle it controlled the exit of food. The significance of cardia was discussed by 

 Fabricius (1618) who cites Galen as stating that the upper orifice of the stomach is 

 called the heart because the symptoms to which it gives rise are similar to those which 

 sometimes affect the heart, sometimes even the brain; but for Fabricius, cardia, as 

 applied to this orifice, merely indicates a chief part of the body. The stomach as a 

 whole is termed gaster, from the Greek, but the Latin ventriculus was generally used 

 by the early anatomists. Although flaccid and shapeless when seen in the dissecting 

 room, the stomach has a very characteristic form. Its epithelium, from an embryo 

 of 44.3 mm., is shown in Fig. 244, and an adult stomach is seen in Fig. 250. It is a 

 tube which is greatly distended toward the left, where its border forms the greater 

 curvature; its right border is the lesser curvature. As a whole the stomach is divided 

 into two parts, the cardiac portion (pars cardiaca) and pyloric portion (pars pylorica). 

 This fundamental subdivision occurs in many animals, as was recognized by Sir 

 Everard Home in 1814. The pyloric part is relatively long in the embryo. It becomes 

 subdivided into the pyloric vestibule and the pyloric antrum. The latter is its smaller 

 part extending to the pylorus; between the two, on the greater curvature, is the sulcus 

 intermedius, well shown in Fig. 250. (The term pyloric antrum has been variously 

 employed, since in its original description by Willis (1674) the vestibule is not recog- 

 nized; Cowper (1698) applies antrum to the terminal subdivision as above defined.) 

 The cardiac part of the stomach is divided into a main portion, or body of the stomach 

 (corpus gastri], and a blind pouch, formerly called the saccus caecus, but now less 



