CHEOl^OLOGICAL TABLE 



OF 



THE DEVELOPMENT OF THE FCETUS. 



(The following table is translated from the work of Beaunis and Bouchard, 

 with some very unimportant alterations. 1 It will serve to present a resume of 

 the preceding facts in an easily accessible form.) 



End of second week. Formation of the amnion and umbilical vesicle. Chorda dorsalis and 

 medullary groove. Heart. 



Beginning of third week. The vitelline membrane has entirely disappeared. Protovertebral 

 disks. First pharyngeal arch. Buccal depression. Primitive circulation. 



End of third week. The allantois and Wolffian body appear. The amnion is closed. Cerebral 

 vesicles. Primitive ocular and auditory vesicles. Coalescence of the inferior maxillary 

 protuberances. Liver. Formation of the three last pharyngeal arches. 



Fourth week. The umbilical vesicle has attained its full development. Projection of the caudal 

 extremity. Projection of the upper and lower limbs. Cloacal aperture. The heart sepa- 

 rates into a right and left heart. Spinal ganglia and anterior roots. Olfactory fossae. 

 Lungs. Pancreas. 



Fifth week. Vascularity of the allantois in its whole extent. First trace of hands and feet. 

 The primitive aorta divides into primitive aorta and pulmonary artery. Conduit of Mliller 

 and genital gland. Ossification of clavicle and lower jaw. Cartilage of Mcckel. 



Sixth week. The activity of the umbilical vesicle ceases. The pharyngeal clefts disappear. 

 The vertebral column, primitive cranium and ribs assume the cartilaginous condition. 

 Posterior roots of the nerves. Membranes of the nervous centres. Bladder. Kidneys. 

 Tongue. Larynx. Thyroid gland Germs of teeth. Genital tubercle and folds. 



Seventh week. The muscles begin to be perceptible. Points of ossification of the ribs, scapula, 

 shafts of humerus, femur, tibia, intermaxillary bone, palate, upper jaw (its first four points). 



Eighth week. Distinction of arm and forearm, and of thigh and leg. Appearance of the inter- 

 digital clefts. Capsule of the lens and pupillary membrane. Completion of the interven- 

 tricular and commencement of the interauricular septum. Salivary glands. Spleen. Su- 

 prarenal capsules. The larynx begins to become cartilaginous. All the vertebral bodies 

 are cartilaginous. Points of ossification for the ulna, radius, fibula, and ilium. The two 

 halves of the bony palate unite. Sympathetic nerve. 



Ninth week. Corpus striatum. Pericardium. Distinction between ovary and testicle. Forma- 

 tion of the genital furrow. Osseous nuclei of vertebral bodies and arches, frontal, vomer, 

 malar bone, shafts of metacarpal bones, metatarsal bones and phalanges. The union of the 

 hard palate is completed. Gall-bladder. 



Third month. Formation of the foetal placenta. The projection of the caudal extremity disap- 

 pears. It is possible to distinguish the male and female organs at the commencement of the 

 third month. The cloacal aperture divided into two parts. The cartilaginous arches on 

 the dorsal region of the spine close. Points of ossification for the occipital, sphenoid, os 

 unguis, nasal bones, squamous portion of temporal and ischium. Orbital centre of superior 

 maxillary bone. Commencement of formation of maxillary sinus. Pons Varolii. Fissure 

 of Sylvius. Formation of eyelids and of hairs and nails. Mammary gland. Epiglottis. 

 Union of the testicle with the canals of the Wolffian body. Prostate. 



Fourth month. The closure of the cartilaginous arches of the spine is complete. Osseous 

 points for the first sacral vertebra and pubes. Ossification of the malleus and incus. 

 Corpus callosum. Membranous lamina spiralis : cartilage of the Eustachian tube. Tym- 

 panic ring. Fat in subcutaneous cellular tissue. Tonsils. Closure of genital furrow and 

 formation of scrotum and prepuce. 



1 It will be noticed that the time assigned in this table for the appearance of the first rudiment 

 of some of the bones (e. y., the ilium) varies in some cases from that assigned on p. 52. This is 

 a point on which anatomists differ, and which probably varies in different cases. 



\ 112 



