acinous fibrous tissue and communicate with the glands of the axilla.

The milk consists of a clear fluid, suspended in which are immense numbers of oil droplets, together with some granular matter from the cells lining the acini and tubules.

During the first few days of lactation certain large, granular, fatty, highly refracting bodies occur, which have received the name of colostrum corpuscles.

Fig. 49.-Elements of milk: a, Droplets of oil in milk; b, leukocytes; c, large colostrum corpuscles.

QUESTIONS FOR CHAPTER XI.

244. Describe the general characteristics of the ovary.

245. What is the germinal epithelium? the primordial ova? 246. What is the tunica albuginea?

247. What is the ovarian stroma?

248. What are the Graafian follicles? Where do they originate? 249. Give the structure of the mature Graafian follicle.

250. Describe a corpus luteum.

251. Describe the ovum.

252. Name the layers of the Graafian follicle and ovum in their sequence.

253. Describe the blood-supply of the ovum; the lymphatic; the

nerve.

254. Describe the parovarium.

255. Describe the Fallopian tube; give its structure.

256. Name the coats of the uterus. Describe each.

257. Describe the uterine glands.

258. Describe the cervix.

259. What are the ovulæ Nabothi?

260. Describe the blood distribution of the uterus; the lymphatics; the nerves.

261. Name the coats of the vagina. Describe each.

262. Give the blood-, lymph-, and nerve-supply.

263. Describe the labia majora, the labia minora, and the clitoris.

264. What are the glands of Bartholin?

265. What type of glands are the mammary glands?

266. Describe them.

267. Give their blood- and lymphatic supply.

268. Describe the milk.

269. What are colostrum corpuscles?

CHAPTER XII.

THE RESPIRATORY SYSTEM.

THE larynx is lined with stratified ciliated epithelium, resting on a thin membrana propria of fibroelastic tissue. Beneath this is the submucosa of fibrous tissue, which contains numerous branched tubular glands communicating with the surface. In the external portion of the submucosa are the cartilages of the larynx. Those of the thyroid, cricoid, and arytenoid are of the hyaline variety, the epiglottis and the cartilages of Wrisberg and Santorini being of the yellow, elastic variety.

The trachea is lined with stratified columnar epithelium resting upon a tunica propria. Numerous small racemose glands dip down from the surface into the submucosa below. The submucosa is surrounded by the fibrous coat, embedded in which are a number of C-shaped plates of hyaline cartilage, which surround the trachea on all sides except at its juncture with the esophagus, and which serve to keep the tubes open. External to the cartilage is a slight layer of circular, smooth muscle.

The larger bronchi continue the structure of the trachea, dividing repeatedly until the smaller tubes are reached, when the cartilage rings become smaller and smaller, until they entirely disappear. The epithelium is reduced to a single layer and the muscular coat becomes relatively better developed.

THE LUNGS.

The smaller bronchi divide until the terminal bronchi are reached, the diameter of each of which is about 1 mm. (1 inch). These, again, branch to form

Fig. 50.-Bronchial tube: a, Mucous membrane; b, muscularis mucosa; c, cartilage plate; d, lung tissue; e, small artery; f, bronchial gland; g, duct of bronchial gland.

narrow tubules, the alveolar ducts, which open into dilated pouches, called the infundibula, from which again a number of air-sacs or alveoli open.

The alveolar ducts are lined with nonciliated low columnar cells lying on thin, fibrous, elastic basement membrane.

The alveoli are lined with a single layer of epithelium.

The groups of acini belonging to a terminal bronchus are united to a number of similar groups by fibro-elastic tissue to form a lobule.

Fig. 51.-Diagram of bronchial terminations: a, Smaller bronchus; b, terminal bronchus; c, alveolar duct; d, constriction, or neck; e, space of infundibulum outlined by dotted lines; f, infundibula; g, ciliated columnar cells lining small bronchus; h, nonciliated columnar cells lining alveolar ducts; i, flat epithelium lining alveoli.

Numerous lobules are similarly united to form the lobes, the external surface of which are covered by a serous membrane, the pleura.

The blood-vessels follow the course of the bronchi, dividing into a capillary network in the alveolar walls