ANATOMY OF A 17.8 MM. HUMAN EMBRYO 45 



dorsal pancreas, the ventral also shows a branching condition of 

 its epithelium. The duct of the ventral pancreas (D.panc.v.) is 

 short, and opens into the bile duct (Dxhol.) near its entrance into 

 the duodeniun. 



RESPIRATORY SYSTEM 



The olfactory pits are described with the sense organs. 



The entodermal lining of the larynx and trachea are represented 

 as seen in ventral view in plate 6; from the left side in plate 2; 

 and in the median sagittal section in plate 1. In plate 1 the 

 anlage of the right lung is seen from the left side. 



Larynx. The larynx, which opens from the pharynx by a 

 T-shaped aperture, is placed immediately caudal to the epiglottis. 

 The pedicle of the T or interarytaenoid notch, extends dorso- 

 ventrally between the arytaenoid protuberances, and is bounded 

 laterally by the ary epiglottic folds. A median raph6 (R.) ex- 

 tends dorso-ventrally across the larynx, in a somewhat caudal 

 direction, so as to close it temporarily. 



Trachea. The trachea passes caudally to bifurcate into the 

 two bronchi. The root of the left bronchus is shown in section 

 in plate 1 (Br.s.) but, the greater portion of this bronchus and 

 the corresponding lung have been removed. 



Lungs. The entodermal outpocketings of the right lung and its 

 pulmonary vessels (A.pul. and Vp.pul.d.) are represented in plate 

 1, as seen through the mediastinum. An eparterial (tracheal) 

 bronchus is present on the right. It is situated dorsal to the 

 right pulmonary artery, and a branch of the latter passes ceph- 

 alad of this bronchus. The oesophagus (Oe.) passes between the 

 developing lungs. 



Pleural cavity. Each pleural cavity is closed off completely 

 from the pericardial by the pleuro-pericardial membrane, but 

 still communicates with the abdominal cavity. The aperture 

 on the left is very small. 



A blind prolongation of the right pleural cavity begins medially 

 and dorsally to the anlage of the root of the right lung. From 

 here it extends caudally and somewhat ventrally along the right 



