308 ANATOMICAL TEOBNOLOGY. 



tracted. When uncontracted, the dorsal side is fleshy, something 

 like the oesophagus. 



§ 800. Microscopic Structvre of the Trachea. — (A) Its octal layer is of rather dense 

 connective tissue. In it are Imbedded the incomplete rings of ca/rtUage. (B) Entad of the 

 connective tissue layer and extending around about the dorsal third of the circumference 

 of the trachea is a layer of unstriped muscle. This is partly attached to the ectal surface 

 of the rings of cartilage, and by its contraction causes the rings to meet or even overlap. 

 (C) Entad of (A) and (B) is a layer mostly composed of elastic connectiw tissue. (D) Mu- 

 cous membrane. This lines the lumen of the trachea. It is composed of three layers of 

 cells, the free layer of which is ciliated. (E) Imbedded in the vrall of the trachea are 

 many racetnose glands whose ducts open on the free surface of the mucous membrane. See 

 Strieker, A, 435 ; Quain, A, 11, 266. 



§ 801. CEsophagus, as'.— Grullet (Fig. 77, 109).— The oesophagus 

 is the fleshy tube connecting the pharynx and stomach. 



§ 802. Demonstration.— Draw the trachea somewhat dextrad, 

 and there will be seen the oesophagus, an entirely fleshy tube, dor- 

 sad and slightly to the left of the trachea. When empty it does 

 not retain a cylindrical form like the trachea, but collapses. 



§ 803. Structure of the (Esophagus. — (A) The ectal layer is composed of striated mus- 

 cular fibers arranged as in the intestine {§ 741}, with an admixture of vnstriated muscle 

 increasing caudad. (B) The intermediate layer is of connective tissue and forms the syi- 

 mucpsa. It contains many small racemose glands. (C) The ental or mucous layer is 

 •composed of stratified epithelium. See Strieker, A, 361 ; Quain, A, II, 344. 



THORAX. 



§ 804. The thorax or chest is the part of the trunk between the 

 diaphragm and first rib. Its cavity contains the lungs (§ 809), the 

 heart and great vessels (Fig. 91), and part of the trachea and 

 oesophagus (§§ 799, 801 ; see also Chap. VIII). 



§ 805. Exposure. — Determine the position of the following land- 

 marks : presternum (§ 228) ; xipMsternum (§ 228) ; first rib (Fig. 

 30, 72) ; ventrimeson—the line between tbe xiphisternum and prse- 

 sternum. 



Incisions. — ^A. Make a longitudinal incision (§ 599) through the 

 skin and muscles 3 cm. to the right of the ventrimeson from the first 

 rib to a point opposite the base of the xiphisternum. Taking care 

 not to injure the vessels and nerves in the axillary region, reflect 

 the skin for 2-3 cm. on the right of the incision. 



B. Make a transverse incision from the caudal end of the longi- 

 tudinal incision to a point 4-5 cm. to the left of the ventrimeson. 



