Then He was not of truly human form. When one is concieved one takes on the nature of one's mother: the Lord did just that when He was concieved. It is in fact one of the crucial elements of His coming- He took on our very nature, He shared in man-kind's flesh, was of "the descent of David". To suggest that He was merely "through" Mary is really untenable. It suggests that He was somehow of "special" flesh, of angelic or superhuman flesh.
Jesus did not merely "pass through" Mary; He became very flesh of mankind's flesh, having a real mother: He truly came in the flesh, though through the agency of the Holy Spirit. Even in birth we see His complete Godhood and complete Manhood- of Mary and of God. Thus is His salvific work, which continues in Him: True God and True Man, glorified, uniting us men unto God through Him.
well said and spot on.