On harelip and cleft palate

by William Rose

About the sixth week the stomodæum shows signs of division into upper and lower segments by the outgrowth from the deep aspect of each maxillary process of horizontal palatal plates, which by their junction in the median line form the rudiments of the hard and soft palate, separating thus the nasal and buccal cavities. The anterior portion of these unite with the lateral aspects of the deeper parts of the fronto-nasal process, leaving a space of greater or less dimensions in the median line, known as the anterior palatine canal, which serves subsequently for the passage of nerves and vessels, and for the lodgment of the “organ of Jacobson” in animals in which it occurs.

The upper or nasal cavity is again subdivided into lateral halves by the growth downwards from the under surface of the fronto-nasal process of a central vertical septum, to become in time the cartilaginous septum nasi and the bony ethmo-vomerine plate, uniting at its lower border with the primary fleshy palatine processes ([Fig. 34]).

The tongue grows as a fleshy protuberance from the floor of the stomodæum; antero-lateral segments on either side from the conjoined second and third branchial arches unite with a central posterior growth from the tuberculum impar in an inverted 𝖸-shaped manner. At the point of junction of the segments is a depression from which the thyroid gland develops, indicated in later life by the foramen cæcum.

Fig. 34.—Diagrammatic representation of the development of the palatal processes and of the ethmo-vomerine plate, seen in vertical section. (After Gegenbaur.)

a. Ethmo-vomerine plate. b. Palate processes. c. Tongue. d. Buccal cavity. e. Nasal cavity.

Each of these primary epiblastic pits is at a later date almost entirely cut off from its connection with the buccal cavity. The external and internal nasal processes of the fronto-nasal outgrowth unite below the anterior olfactory pits, and thus surround the anterior nasal apertures, and separate the nares from the mouth. The external nasal and superior maxillary processes are also freely amalgamated except along one small deep track, which remains patent to form the nasal duct and lachrymal passages; and probably the internal nasal and maxillary processes unite below the external nasal process to establish the continuity of the red margin of the upper lip. The union of all these various parts has been completed by the sixth to the tenth week of normal fœtal life; the external nasal and superior maxillary processes unite first, and by the sixth week are becoming closely approximated to the central portion of the fronto-nasal process, a time when the palatal processes are only indicated as slight ridges. By the ninth week the alveolus and upper lip are complete, and union of the palate is commencing from before backwards, being usually completed even to an indication of the uvula by the tenth week.

Whilst the later stages of these developmental processes are in progress, points of ossification have been appearing in many places to form the cranial and facial skeleton. A full knowledge of this subject is still unattained, but the researches of Goodsir, His, and others have thrown much light on hitherto dark passages. There are two main sources of origin of the bones of the skull, viz. from cartilage and from membrane, and it is important to appreciate the portions of the skull which originate from each of these sources respectively. The bones laid down primarily in cartilage are mainly those forming the base of the skull and their anterior prolongations. Thus about the fourth week of intra-uterine life the basis cranii consists of a cartilaginous mass surrounding the upper end of the notochord, and prolonged anteriorly around the pituitary fossa as two cartilaginous bars, the trabeculæ cranii, into the fronto-nasal process. From the anterior extremity of this the nasal bones and cartilages are developed, and from the under surface the ethmo-vomerine plate. The transformation of the primordial mesoblastic undifferentiated tissue into recognisable cartilage is occurring from about the fourth or fifth week until the eighth, when ossification at different centres is apparent. To the development of the intermaxilla we shall refer in detail later; suffice it to say here that the ossifying centres appear about the eighth week, and by the twelfth to the fourteenth the whole process is ossified, and the space between the maxillæ closed except posteriorly, where the anterior palatine canal remains permanently patent; the component parts of the bone, however, are not united until a later date. There are two other cartilaginous foci from which ossification ensues, viz. the pterygo-palatine cartilage in the superior maxillary process, a delicate bar from which arise in part the pterygoid and palatine plates; and Meckel’s cartilage in the mandibular process for the production of the mandible and malleus. All the other facial bones are developed from membrane, more or less in connection with these bars. The vomer is ossified from a single nucleus appearing in the upper part of the ethmo-vomerine plate, about the ninth week; from this two laminæ are developed, which, passing downwards and forwards on either side of the middle line, embrace the septal cartilage. The amount of the osseous material increases from behind forwards, until at maturity a median osseous lamina remains which is grooved only anteriorly.

The palate bone develops from a single centre appearing about the eighth week at the junction of the horizontal and perpendicular portions. The superior maxilla is supposed to arise from four separate foci of ossification, viz. for the alveolar arch, for the palate, for the orbito-malar portion, and for the naso-facial segment. All these are united together by the third month.

It is unnecessary here to discuss the development of the teeth beyond stating that the thickening of the epiblast covering the gums, which occurs as the earliest sign of the production of the milk teeth, is to be seen about the forty-fifth day, when as yet there are no signs of ossification of the maxilla, and by two and a half months a distinct involution filled with cells is evident. Calcification commences about the eighteenth week of intra-uterine life, and extending from crown to fang is usually not completed until from twelve to twenty months after birth.