124 DEVELOPMENT OF PRIMITIVE BLOOD-VESSELS. 



PLATE 7. 



Injection of the vessels of the brain of an embryo pig measuring 6.5 mm. in length after fixation and dehydration. 

 The injection is a complete one, but the vessels of the visceral arches and most of the vessels of the cerebrum 

 have been omitted in the drawing. The figure shows, first, the longitudinal artery of the central nervous 

 system, which extends from the tip of the carotid artery to the caudal tip of the spinal cord; this artery is a 

 plexus opposite the subthalamus, a single vessel down to the lower part of the medulla, and again a plexus 

 on the cord; second, a part of the capillary plexus which invests the entire neural tube; third, the relation 

 of the primitive veins of the forebrain, the midbrain, and the hindbrain to the vena capitis prima. X73. 

 A. &., a. basilaris; a. c. l,a.. carotis interna; a. 1, artery to the medulla in the first interspace; a, m. p., 

 a. maxillaris primitiva; v. cap. p. 1, v. capitis prima, first or cerebral segment, which drains the forebrain and 

 midbrain; v. cap. p. 2, \. capitis prima, second segment, which is shown only in outline, and which drains 

 the forebrain, the midbrain, the hindbrain, and the visceral arches; v. cap. p. 3, v. capitis prima, third 

 segment, which is the anterior cardinal vein and which drains the brain and the visceral arches; v. m. p., 

 v. maxillaris primitiva; ves. a., vesicula auditiva; 3, 4i an d 6, third, fourth, and sixth aortic arches, which are 

 coming from the heart and are leading to the descending aorta, which is concealed by the cardinal segment 

 of the vena capitis prima; V, position of the root of the n. trigeminus; VIII, position of the roots of the 

 nn. cochlearis et vestibularis; IX, position of the root of the n. glosso-pharyngeus; A', position of the root of 

 the n. vagus; XII, position of the root of the n. hypoglossus. 



